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AQA BIOLOGY A LEVEL > 2.4 CELL RECOGNITION AND IMMUNE SYSTEM > Flashcards

2.4 CELL RECOGNITION AND IMMUNE SYSTEM Flashcards

1
Q

What is an antigen?

A

A molecule that triggers an immune response. They vary depending on the pathogen, and can be responsible for causing disease.

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2
Q

What types of defence mechanisms does the body have against pathogens? (2)

A
  • Specific

- Non-specific

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3
Q

Outline examples of the non-specific response.

A

Faster as it is the same for all pathogens.

  • Physical barriers, ie skin
  • Phagocytosis
  • Chemical barriers, ie enzymes/acid.
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4
Q

Outline examples of the specific response.

A

Slower, but specific to each pathogen.

  • T cell mediated response
  • B cell humeral response
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5
Q

What is phagocytosis?

A

When phagocytes (WBCs) trap and destroy pathogens.

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6
Q

Outline the process of phagocytosis.

A
  1. Phagocytes are attracted to pathogens and then they stick to this same pathogen.
  2. The phagocyte then engulfs the pathogen to form a phagosome.
  3. The phagosome then binds to a lysosome to form a phagolysosome.
  4. Lysosomes release the digestive enzyme lysozyme, destroying the pathogen by hydrolysing their cell wall.
  5. What can be digested, is digested.
  6. Whats left of the pathogen (indigestible) forms the residual body which is later discharge from the phagocyte.
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7
Q

What is the cell mediated response?

A

T lymphocytes respond to body cells after the invasion of a foreign antigen.

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8
Q

Where do T cells mature?

A

In the thymus gland

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9
Q

What are T cells?

A

Specific T lymphocytes (WBC)

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10
Q

Outline the process of the cell mediated response.

A
  1. Microphages take in pathogens by phagocytosis, and display their antigens on their cell surface.
  2. Receptors on T HELPER cells bind to the antigens, stimulating the cloning of T HELPER cells by mitosis.
    3a) some cloned T cells stimulate phagocytes to engulf more pathogens by phagocytosis.
    3b) forms CYTOTOXIC T CELLS, which destroy infected cells using ‘perforin’ which makes holes in their cell membranes.
    3c) forms some MEMORY T cells, so can have a faster response if this pathogen is met again.
  3. Finally, it stimulates B cells to divide for the humeral response.
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11
Q

Where do B cells mature?

A

In the bone marrow

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12
Q

Outline the B cell humoral response.

A
  1. B cells have antibodies which bind to complementary antigens on pathogens.
  2. This causes the antigen to be taken up by endocytosis and presented on the B cells’ surface.
  3. These make microphages for the cell mediated response.
  4. After this, B cells divide by mitosis to form:
    a) Plasma B cells, which make the antibodies to destroy the pathogens antigen (primary response)
    b) Memory cells which stay in the blood, so can quickly form plasma cells if in contact with the same pathogen again. (secondary response)
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13
Q

What is an antibody?

A

A protein produced by B cells to counteract a specific antigen.

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14
Q

What is the structure of an antibody?

A
  • Made of 4 polypeptide chains in a ‘Y’ structure.
  • Have 2 heavy chains, and 2 light chains.
  • At the end of each stem of the Y, is the variable region.
  • The variable region is a binding site that is specific to antigen.
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15
Q

What is the antibody-antigen complex?

A
  • A specific antigen joins to the antibody’s binding site.

- This has H bonds and hydrophobic interactions at the variable region, to form the complex.

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16
Q

How do antibodies destroy antigens?

A

Agglutination and then phagocytosis

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17
Q

Outline the process of agglutination and then phagocytosis.

A

Each antibody has 2 binding sites. So multiple antigens can bind to a single antibody, clumping them together so they are easier to engulf during phagocytosis.

18
Q

What is active immunity?

A

When an individual makes their own antibodies, it is slow but long lasting.

19
Q

What is passive immunity?

A

When antibodies are given, it is an immediate response but has no long term benefits.

20
Q

What is artificial immunity?

A

When the response in stimulated from an external body (ie vaccines)

21
Q

What is natural immunity?

A

When the immune response is triggered organically, by exposure to disease/

22
Q

What is a vaccine?

A

A weak/dead pathogen given orally or by injection to stimulate an immune response and create memory cells.

23
Q

What is herd immunity?

A

When a large percentage of the population are vaccinated, is it reduces the chance of people (non-vax) coming into contact with the pathogen and falling ill.

24
Q

What do vaccines do?

A

They trigger an immune response, so that a secondary response can occur quickly (before symptoms show) if ever faced with that pathogen again.

25
Q

What are monoclonal antibodies?

A

A highly specific antibody that is made outside of the body, and recognised only 1 pathogen (antigen).

26
Q

What are the uses of monoclonal antibodies?

A
  • Medical diagnosis

- Treatments

27
Q

How can monoclonal antibodies be used in medical diagnosis?

A

If antigens are present, the monoclonal antibody will bind to them and test positive. This will be due to the formation of an antibody-antigen complex.

28
Q

How can monoclonal antibodies be used in treatment?

A

Specific antibodies can attach to specific cells, ie in cancers, to block the uncontrolled growth. This will benefit as it won’t destroy healthy cells. Provides a very targeted approach to treatment.

29
Q

What are the ethical concerns surrounding monoclonal antibodies?

A
  • Production involves mice. (kills them)
  • Doesn’t come without risks, so need to obtain informed consent before the procedure.
  • Need to have human clinical trials, which could affect volunteers in unknown ways and so is a controversial topic of discussion.
30
Q

What are the ethical concerns surrounding vaccines?

A
  • Can be very expensive.
  • Risk of getting it may outweigh the benefits.
  • Could have bad unknown side effects.
  • Need to be tested on animals.
  • Need to have human clinical trials, which could affect volunteers in unknown ways and so is a controversial topic of discussion.
31
Q

What is the structure of HIV?

A
  • Has attachment proteins.
  • Has a lipid envelope.
  • Inside is filled with a matrix.
  • Has an capsid.
  • Contains RNA and reverse transcriptase enzyme.
32
Q

What is a retrovirus?

A

Has the reverse transcriptase enzyme, so can make DNA from RNA.

33
Q

In which cells does HIV replicate?

A

Helper T cells (hT)

34
Q

Outline the process why which HIV replicates.

A
  1. HIV bonds to CD4 protein on hT cells.
  2. HIV and hT fuse, so RNA and RT enzymes enter the hT cell.
  3. Inside the hT cell, RNA is converted to DNA.
  4. The DNA enters the hT nucleus, and the cell’s DNA.
  5. This makes new mRNA, and undergoes protein-synthesis to make new HIV particulates.
  6. New HIV particles then break away from the hT, using some of its’ membrane to form a new lipid envelope.
  7. This destroys hT cells.
35
Q

How does HIV evolve into AIDs?

A
  • hT cells are destroyed
  • Ruins the immune response, as it can’t produce antibodies or cytotoxic T cell anymore.
  • Vulnerable immune system.
  • Easy to catch infections that lead to AIDs.
36
Q

How do you test for HIV?

A

The enzyme linked immunoabsorbant assay (ELISA) testing.

37
Q

What does the ELISA test show?

A
  • if HIV was ever encountered
  • if a person is infected by HIV
  • the severity of HIV (due to conc of antigens)
38
Q

Outline the process of the ELISA test.

A
  1. Take a sample, and wash it to remove unwanted antigens.
  2. Add a monoclonal antibody specific to HIV to the sample.
  3. After some time, add a 2nd antibody (labelled with an enzyme) which can bind to the 1st antibody.
  4. Add a colourless substrate, which will change colour when an E-S complex forms.
  5. The amount of antigens present, will be depicted by the intensity of the colour.
39
Q

How do antibiotics work in bacteria?

A
  • Inhibit an enzyme that makes cell walls.

- This causes bacteria cells to burst, be destroyed, and therefore die.

40
Q

Why do antibodies not work for viruses?

A
  • Viruses don’t have cell walls.

- So the antibiotic process would make no difference.

41
Q

What can be used instead of antibiotics for viruses?

A

Antiretrovirals (used to keep HIV replication low)

AQA BIOLOGY A LEVEL (38 decks)

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